Browsing by discipline "Fysik"
Now showing items 61-80 of 104
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(Helsingin yliopistoHelsingfors universitetUniversity of Helsinki, 2012)Cellulose is the most abundant natural material on Earth. New ways to utilize the limited resources on Earth for the benefit of the human kind can be found by studying genetically modified plants. The nanoscale structure of organic matter is important to its macroscopic properties. Natural materials can be characterized by measuring the degree of crystallinity in the material and the average dimensions of the crystallites. The cellulose crystallites are helically wound as long fibrous microfibrils in which crystalline and less ordered (amorphous) regions alternate. The microfibril angle (MFA) is the angle of these microfibrils with respect to the cell axis and it is linked with the longitudinal stiffness of the material. A wide-angle X-ray scattering (WAXS) method can be used to study these nanoscale properties of the matter in a non-destructive manner. Arabidopsis thaliana (AT) is an important model system for plant biology. It is a widely spread small flowering plant with a short life cycle and a relatively small genome which has been fully sequenced. X-ray microtomography confirmed that the AT cells are generally round rather than rectangular unlike xylem cells. The cellular structure of the plants was not destroyed in the WAXS measurements. The resolution obtained from the measurements of samples with natural humidity was not sufficient hence all the samples were measured dry. A total of 62 samples were measured with the WAXS set-up, 15 of them wild type plants and the rest genetically modified. In this study the WAXS data analysis methods were enchanced for the benefit of the weakly scattering Arabidopsis samples. The mean crystallite width of all samples ranged from 26 to 30 Å. This is consistent with the crystallite width being determined during the biosynthesis of cellulose. The values for the degree of crystallinity ranged from approximately (20 30)% and all the average values were slightly above 25%. The mean microfibril angle varied greatly between the samples, all the way from 2 to 21 degrees. The mean values of different lines varied more for the MFA than for other properties. Statically significant differences between means of different lines were seen for one line in the degree of crystallinity, for one line in the MFA and for two lines in the crystallite width. Due to small sample sizes these differences should be considered mostly as indicative and not as conclusive evidence on the effects of the genetic modification.
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(Helsingin yliopistoHelsingfors universitetUniversity of Helsinki, 2016)Ilmakehässä tapahtuvan hiukkasmuodostuksen ymmärtämiseksi tarvitaan mittalaitteita, joilla voidaan mitata hiukkasia heti vastamuodostuneista aerosolihiukkasista lähtien. Aivan pienimpien aerosolihiukkasten mittaaminen asettaa monenlaisia haasteita mittaukselle sekä mittalaitteille. Seikat, kuten lämpötila, ilmankosteus ja hiukkasten kemiallinen koostumus, vaikuttavat mittaustuloksiin. Tässä työssä pyrittiin selvittämään miten paljon näyteilman kosteus vaikuttaa dietyleeniglykolia käyttävän hiukkaskasvattimen mittaustuloksiin. Tutkimuskohteena oli Airmodus A10 hiukkaskasvatin(PSM), jossa hiukkaset kasvatetaan dietyleeniglykolihöyryllä niin, että ne voidaan tämän jälkeen laskea perinteisellä kondensaatioydinlaskurilla. Käyttämällä dietyleeniglykolia kasvatuksen ensimmäisessä vaiheessa pystytään mittaamaan hiukkasia noin 1 nanometrin kokoisista hiukkasista lähtien. Tutkimuksen aikana tuotettiin kokoluokiteltu ja kemialliselta koostumukselta tunnettu näyteaerosoli, jonka avulla laitteen havaintotehokkuus mitattiin vertailulaitetta vasten. Laitteen leikkausraja ja havaintotehokkuus mitattiin kahdella erilaisella näytteellä erilaisissa näyteilman kosteuksissa. Mittauksissa käytetyt hiukkaset tuotettiin putkiuunilla kiinteästä ammoniumsulfaatista ja sähkösumuttamalla metanoliin liuotetusta tetraheptyyliammoiumbromidista(THABr) ja tetrapropyyliammoniumjodidista(TPAI). Kokeellisten mittausten perusteella näyteilman kosteudella on selvä vaikutus laitteen toimintaan. Samoilla laitteen toimintaa määrittävillä virtaus- ja lämpötila-asetuksilla laitteella voidaan mitata pienempiä hiukkasi, jos näyteilman kosteus on suurempi. Laitteen kalibrointi, leikkausraja-saturaattorivirtauksen funktiona, siirtyi 0.2 - 0.3 nanometriä näyteilman kosteuden kasvaessa 1 - 40 % huoneenlämpötilassa. Leikkausrajan siirtyminen havaittiin kummallakin tavalla tuotetuilla hiukkasilla. Lisäksi havaintotehokkuutta onnistuttiin parantamaan käyttämällä toimintanesteenä puhtaan dietyleeniglykolin sijaan vesi-dietyleeniglykoli-liuosta. Kokeellisten mittausten lisäksi näyteilman kosteuden vaikutuksia pyrittiin selvittämään simuloimalla laitteen virtauksia COMSOL muptiphysics -ohjelmalla. Mallinnettujen lämpötilojen, virtausten ja höyryjen pitoisuuksien avulla laskettiin nukleaatiotodennäköisyys ja Fletcherin halkaisija eri näyteilman kosteuksissa. Simulaation mukaan vesihöyryn pitoisuus osassa, jossa mitattavat hiukkaset aktivoituvat, on niin suuri, että se vaikuttaa nukleaatiotodennäköisyyteen. Tämän perusteella havaittu efekti ei kosketa vain kyseistä laitetta vaan muitakin dietyleeniglykolia käyttäviä hiukkaslaskureita.
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(2017)Light scattering measurements are important for characterizing small particles. The scattering data can replace simplified theoretical models in simulations, e.g. Mie scattering, providing significantly more realistic simulation results. It can also be used as a standard, to which more advanced scattering models can be compared. We present a new instrument for measuring light scattered by micrometer- to millimeter-sized particulate samples, which are levitated ultrasonically. The instrument was built within the scope of this project. While other setups exist that can measure light scattering, our instrument is unique in its capability to measure individual particles which are held in place in mid-air. The system is measures light of multiple wavelengths, scattered in 360 degrees and taking light polarization into account. Samples are held in place by a Langevin-type ultrasonic levitator, which eliminates any stray scattering from a sample holder, while simultaneously making the measurement non-destructive and non-contacting. The non-destructive measurement allows for research on valuable and unique samples, such as rare meteorites and space dust. In this work, we detail the design principles of our instrument, as well as its calibration. We estimate its performance by measuring scattering from clear glass spheres and comparing the results to Mie scattering simulations. We also demonstrate the instrument's capability to handle real samples by measuring the light scattering properties of a rock sample taken from the Chelyabinsk meteorite. The measurements show that our instrument provides accurate light scattering data from a variety of samples. This makes it a valuable tool which can be used to validate theoretical models and provide unique light scattering data from samples that would otherwise be hard to measure.
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(Helsingin yliopistoHelsingfors universitetUniversity of Helsinki, 2011)We present the results of a numerical simulation of energetic proton propagation in a model of Hermean magnetic field. The analysis is in connection with the scientific work of the particle detector of the Solar Intensity X-ray and particle Spectrometer (SIXS) on-board BepiColombo, which is to be launched in 2014. In this work we have used a test particle simulation model developed by Vainio and Sandroos of the University of Helsinki. Mercury's environment is a complex system, resulting from the interaction between the solar wind, magnetosphere, exosphere and surface. The mission BepiColombo, a joint project of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) will be equipped with scientific instruments for detailed observation of Mercury's magnetic field and the magnetosphere. SIXS will investigate the direct solar X-rays and energetic proton and electron fluxes in the planet's environment. The flux distribution of energetic protons on the surface of Mercury and in the magnetopause is studied at different locations of the simulated BepiColombo/MPO like orbit around the planet. Two primary simulations were carried out: first, an orbit with periherm 2840km and apoherm 3940km and second, a surface skimming circular orbit. Motivation for circular orbit was to understand the distribution at the magnetopause of particles hitting the surface of the planet as viewed from above the surface on the noon-midnight meridian. The response of several energy levels of particles to different locations in the static magnetic field is studied by analysing latitude-longitude maps of flux distribution and asymptotic directions through various widths of instrument view cone. SIXS experiment uses five such view cones. The view cone, which is approximately in the anti-nadir direction, was targeted in the simulation. Data were compiled at locations with a 30 degree separation (with respect to latitudinal plane) along the orbits. Interpretation of the data was realised though a few MATLAB® subroutines and functions. The results suggest that SIXS is capable of providing data from targeted areas to perform relevant and specific tasks for MIXS (Mercury Imaging X-ray Spectrometer) as expected and planned. It was found out that in order to accurately describe certain propagation behaviours we need to improve the simulation to have the ability to map the path of a specific particle. Concise summaries of the planet Mercury, BepiColombo mission and Solar Energetic Particles have been provided along with supporting appendices. Also the basic principles behind important numerical techniques used have been introduced.
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(2016)Atmospheric new-particle formation (NPF) is an important source of climatically relevant aerosol particles. Observations show that local scale variation in the number concentration of freshly formed particles is common inside the boundary layer. This variation remains poorly understood. The aim of this study was for the first time ever to identify, characterize and explain the dominant local scale spatial variation in the number concentration of nucleation mode particles over a rural boreal forest region by analyzing airborne and sufrace-based measurements. The airborne measurements utilized an instrumented Zeppelin NT airship and a light Cessna 172 airplane. The measurement flights took place around the SMEAR II field station in Hyytiälä, Finland between the years 2013–2015. Number-size distributions and number concentrations of aerosol particles were measured down to nucleation mode sizes and the meteorological conditions were surveyed. The most important inhomogeneities, in terms of increase in the number concentration and commonness, were found to be long, less than 10 km wide, boundary layer deep regions of nucleation mode particles that were roughly aligned with the mean flow. These regions were named NPF streets. The number concentration within the NPF streets could increase between 2...10 fold compared to the surroundings. At least one NPF street was observed over the measurement area on at least 43 % of the NPF event days measured. On May 8, 2013 the particle growth rate in the NPF street and in the concurrent regional NPF event was similar (~2 nm/h). Particle growth inside the small measurement area indicates that the particles were forming simultaneously along the length of the NPF street. The NPF streets were found to be linked to horizontal roll vortices due to roll-enhanced NPF. However, only some (adjacent) rolls were able to enhance NPF significantly. Because of the large horizontal scale of roll vortex systems and NPF events, coupled with the relatively large increase in number concentration and commonness, the NPF streets might be an important source of aerosol particles over the boreal forest.
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(2013)The electric solar wind sail (E-Sail) is a space propulsion invention exploiting the dynamic pressure of the solar wind. It uses centrifugally stretched positively charged conductive tethers to create thrust from the momentum flux of the solar wind. In space the tethers must be micrometeoroid resistant. We use ultrasonic bonding to create an aluminum multiwire Heytether structure to address this issue. For this work we produced a 1 km continuous piece of multifilament E-Sail tether of µm-diameter aluminum wires using a custom made automatic tether factory. The tether comprising 90704 bonds between 25 and 50 µm diameter wires is reeled onto a metal reel. The total mass of 1 km tether is 10 g. We reached a production rate of 70 m/24 h and a quality level of 1 ‰ loose bonds and 2 ‰ rebonded ones. Thus, we demonstrated that production of long electric solar wind sail tethers is both possible and practical. Based on images captured of each bond, a post production analysis was done to determine failure rate and types of the failures that occured during the production.
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(2013)The neutral B_s meson consisting of \mathrm{\bar{b}} and s quarks can decay through the channel B_s → J/ψ Φ The B_s can on-flight mix with its antiparticle \mathrm{\bar{B}}_\mathrm{s} that can also decay to the J / ψΦ final state. The identification of the b quark flavour of the B_s meson at the production time is crucial for measurement of the phase Φ_s, a parameter describing the CP violation between the B_s meson eigenstates. Different types of flavour tagging methods have been developed to extract the initial flavour of decayed neutral B mesons. Since the b quarks at the LHC are produced as b\mathrm{\bar{b}} pairs, one method to identify the B_s flavour is to use muons that originate from decays of hadronised b quarks on the opposite side of the signal meson. In this work, the flavour tagging performance of muons from the opposite-side B hadron decays were studied. The flavour tagging was done for the B_s → J / ψΦ channel and the reference channel B^{+} → J / ψK^{+} with simulated B_s and B^{+} events as well as B^{+} data. This study verifies the flavour tagging performance obtained from simulated B_s events with real B^{+} data since flavour tagging cannot be directly done for B_s events reconstructed from the collision data. The tagging performances obtained from all the three samples are in agreement. The wrong tag fraction of the B^{+} data is (29 ± 0.8) %, the tagging efficiency is (4.03 ± 0.07) % and the tagging power is (0.65 ± 0.04) %. The tagging performance obtained from the B^+ data is compatible with the flavour tagging results obtained by the LHCb experiment.
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(2016)Optimization of contrast enhanced CT (computed tomography) of the intra-abdominal lymphatic system in the case of a chylous leakage is the subject of the study. The chylous leakage means a pathologic condition, where the lymphatic liquid (chyle) leaks out from the vessels of the lymphatic system in intra-abdominal space. The diagnose is rare. CT imaging is based on a different attenuation of the X-rays when they are penetrating through tissues of different kind. Tissues with greater density, like iodine, make the attenuation stronger and they can be used to improve the contrast in the image. Iodinated contrast enhancing agent Lipiodol was chosen for this study for increasing contrast in the CT images of the intestines. The right ratio of the Lipiodol–oil mixing was searched so that the agent would end up in the lymphatic system. The idea was to visualize the lymphatic system and spot the leakage point. This could be useful information when thinking about the follow-up treatment, especially in the case of surgical operation. The examinations were implemented by imaging plastic phantoms with CT device. The CT images were taken with head and torso phantoms, including different mixing ratios of Lipiodol–oil mixtures. The most suitable mixing ratio of Lipiodol and oil was then estimated from the taken phantom pictures. After that, the results were taken in use with two chylous leakage patients, a 70-yearold male patient and a pediatric patient. The CT images of the patients were analysed with ImageJ program. The contrast enhancement when using the Lipiodol contrast enhancing agent was excellent, about 300-400 HU with 120 kV tube voltage. The suitable mixing ratio of the Lipiodol–oil mixture was estimated to be 1:8 with the adult patient and 1:10 with the pediatric patient. The leakage point could not be localized from the CT images. Reason for that might have been the image timing with the pediatric patient. She might have an exceptional rate of fat metabolism, because of her inborn malformations of the intestines. The biokinetical variations and variability of the mixing ratio in the different parts of the intestines also increase the uncertainty of the results of the study. The basic principle of Lipiodol as the contrast enhancing agent has now been tested and the properties of it have been found suitable for similar visualization examinations. The protocol for chylous leakage imaging can be developed and tested further when suitable patients will appear.
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(2018)Deposition is the main removal process of ground-level ozone. In some boreal areas, lakes accounts for up to 30% of the areas. However, there have been only few studies on ozone deposition over lake water in the past forty years. So far only one study has measured the ozone deposition velocity over lake (vd) with the eddy covariance techniques. The 42-day campaign described in this thesis was held in August and September in 2012 in the Lake Kuivajärvi at SMEAR II station in Hyytiälä, Finland. The results showed a mean vd of 0.88±0.05 mm s–1, which was one-fifth of that over forest. vd performed a weak diurnal cycle over lake which had a peak during the nighttime, while the forest showed the opposite. The lake data was classified into daytime and nighttime by a threshold of solar elevation angle (–2°). The two sets of data differed statistically by Mann-Whitney U test. A further analysis showed the higher vd at night might be attributed to the more unstable atmospheric condition. Although, there is no evidence supporting a correlation of vd with stability of the mixing layer in the lake, the dominance of mechanically-induced turbulence appeared to suppress vd. By comparing with previous studies, elevated wind did not facilitate the rate of ozone deposition as expected.
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(2015)Röntgensäteily on monipuolinen modernin materiaalitieteen tutkimusmenetelmä, jolla voidaan tutkia aineen rakennetta makroskooppisesta kokoluokasta aina atomitasolle asti. Tunnetuimpia röntgensäteilyn sovelluksista ovat erilaiset kuvantamismenetelmät, mutta säteilykentän kvantittuminen mahdollistaa myös aineen viritystilojen ja siten sen rakenneosasten keskinäisten vuorovaikutusten tutkimisen. Diffraktio on yleiskäsite ilmiöille, joissa aaltoliike vaikuttaa taipuvan jonkin kohteen vaikutuksesta interferenssin vuoksi. Röntgendiffraktiosta puhuttaessa tarkoitetaan yleensä röntgensäteilyn diffraktiota järjestyneestä aineesta. Säteilyn interferenssistä johtuen röntgensäteilyn diffraktoituminen kiteestä on mahdollista vain tietyillä aallonpituuksien ja sirontakulmien yhdistelmillä. Tämä mahdollistaa röntgensäteilyn monokromatisoinnin ja kohdistamisen esimerkiksi yhtenäiskiteillä, mitä voidaan hyödyntää röntgenspektroskopiassa. Nykyään parhaimman energian erotuskyvyn röntgenspektrometrit perustuvat röntgensäteilyn diffraktioon kiteistä. Kidespektrometri voidaan toteuttaa usealla eri tavalla, joista monet hyödyntävät taivutettuja kiteitä. Eräs yleisesti käytetty kidespektrometrityyppi perustuu niin kutsuttuun Johannin geometriaan, missä tutkittava säteily monokromatisoidaan ja kohdistetaan ilmaisimelle kidekiekolla, joka on taivutettu pallopinnalle. Vaikka Johannin geometria ei ole ideana uusi, pallotaivutettujen analysaattorien heijastusominaisuuksien teoreettinen ymmärrys on ollut viime aikoihin asti puutteellista. Tässä opinnäytetyössä johdetaan lineaarisesta lujuusopista lähtien analyyttinen lauseke pallotaivutetun kidekiekon venymäkentälle ja käytetään sitä yhdessä dynaamisen diffraktioteorian kanssa analysaattorin röntgenheijastusominaisuuksien laskemiseksi. Teorian ennusteita verrataan kahdesta eri piianalysaattorityypistä kokeellisesti määritettyihin heijastuskäyriin. Ennustettujen ominaisuuksien todettiin vastaavan mittaustuloksia erinomaisesti. Teorian lisäksi työssä esitellään siihen pohjautuva, röntgenilmaisimen paikkaherkkyyttä hyödyntävä mittausmenetelmä, jolla on mahdollista parantaa kidespektrometrin energian erotuskykyä menettämättä kuitenkaan näytteestä sironnutta säteilyä. Menetelmän toimivuutta on havainnollistettu sekä simuloidulla että mitatulla röntgenspektridatalla, missä kummassakin tapauksessa saavutettiin tekijän kaksi parannus energian erotuskyvyssä. Teoria ja mittausmenetelmä on julkaistu alan vertaisarvioidussa lehdessä artikkeleissa [J. Synchrotron Radiat. 21:104–110, 2014] ja [J. Synchrotron Radiat. 21:762–767, 2014].
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(2018)Hiukkasten aktivointitodennäköisyys PSM:n sisällä riippuu laitteessa käytettävän kasvattavan fluidin supersaturaatiotasosta siten, että suuremmalla supersaturaatiotasolla saadaan aktivoitua enemmän ja pienempiä hiukkasia. Lisäksi meteorologiset suureet voivat vaikuttaa PSM:n toimintaan. Tämän tutkimuksen tarkoituksena oli selvittää Particle Size Magnifier-mittalaitteen (PSM) herkkyyttä sen asetuksille ja meteorologisille suureille sekä etsiä pienhiukkasmuodostukseen kontribuoivia syitä. Mittausten tarkkuuden kannalta on tärkeää ymmärtää millä PSM:n asetuksilla saadaan mitattua mahdollisimman tarkasti ilmakehän pienhiukkasia kokovälillä 1-3 nanometriä. Tutkimus suoritettiin vertaamalla PSM:n signaalia sekä taustaa eri meteorologisiin suureisiin, hiukkasmittauksiin sekä CI-APi-ToF:lla suoritettuihin höyrymittauksiin. Mittaukset suoritettiin vuosina 2014-2016 SMEAR II-asemalla Hyytiälässä. PSM:n asetuksia säädettiin vuosittain, joten pyrittiin määrittämään optimaaliset asetukset signaali-kohinasuhteen sekä signaalin voimakkuuden kannalta. PSM:n supersaturaation sekä signaalin amplitudin havaittiin laskevan vuosittain ja vastaavasti signaalikohinasuhde parani supersaturaationtason laskiessa. Vuonna 2014 PSM havaitsi selvän päiväsyklin sekä alle 2 nm että 2-3,5 nm hiukkasissa ja päiväsyklin havainnointi vaikeutui sitä seuraavina vuosina. Vuonna 2014 oli myös vahvimmat korrelaatiot CI-APi-ToF:n mittaamien höyryjen kanssa. Kemiallisista yhdisteistä parhaiten PSM:n signaalin kanssa korreloi rikkihappo, ja korrelaatio kaikkien höyryjen kanssa heikkeni supersaturaation heiketessä. PSM:n mittaamilla hiukkaspitoisuuksilla oli myös selkeä korrelaatio lämpötilan ja vesihöyryn pitoisuuden kanssa, mutta tämä saattaa johtua orgaanisten höyryjen vahvasta lämpötilariippuvuudesta. Tuloksista voidaan nähdä, että PSM:n voidaan pitää ainakin tasolla 20-30 hiukkasta per kuutiosenttimetri signaalikohinasuhdetta tai havaintoherkkyyttä merkittävästi vaarantamatta.
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(Helsingin yliopistoHelsingfors universitetUniversity of Helsinki, 2008)Proteiinit ovat elämälle välttämättömiä orgaanisia yhdisteitä, jotka koostuvat yhdestä tai useammasta aminohappoketjusta. Proteiinien toiminnan määrää niiden kolmiulotteinen rakenne, joka taas riippuu pitkälti proteiinien aminohappojärjestyksestä, sekvenssistä. Proteiinien tunnettujen sekvenssien määrä kasvaa DNA-sekvensoinnin tuloksena selvästi nopeammin kuin selvitettyjen kolmiulotteisten rakenteiden, konformaatioiden, määrä. Proteiinien rakenteitakin tunnetaan jo lähes 45 000, joten niiden tilastollisella analyysillä on yhä merkittävämpi osuus uusien proteiinien rakenteen määrittämisessä, ennustamisessa ja suunnittelussa. Työssä etsittiin pentapeptidejä (viiden aminohapon pituisia ketjuja), joilla on sama konformaatio kaikissa tunnetuissa proteiinien rakenteissa. Näitä rakennuspalikoita voisi käyttää suoraviivaisessa proteiinien suunnittelussa halutun kolmiulotteisen rakenteen aikaansaamiseksi. Aineistona käytettiin proteiinitietopankin joulukuussa 2007 sisältämiä rakenteita, joihin kuului lähes 45 000 proteiinin kolmiulotteista rakennetta. Aineiston laajuuden takia rakennuspalikoita etsittiin kahdessa vaiheessa vertailemalla pentapeptidien rakenteen keskeisten atomien (CA, CB, O, C ja N) sijaintia proteiinien aminohappoketjuissa. Työssä löytyi yli 9000 rakennuspalikkaa, pentapeptidiä, joista jokaisella oli sama konformaatio yli 12 eri rakennetiedostossa, niissä ilmoitettujen tarkkuuksien rajoissa. Löydetyistä rakennuspalikoista 48:lla oli täysin sama konformaatio kaikkialla, mistä ne löydettiin. Näistä useimmin esiintyneitä voi käyttää suoraan proteiinien rakenneanalyysissä valmiina kolmiulotteisen rakenteen osina. Eri konformaatioihin laskostuvia identtisiä pentapeptidejä löytyi yli 266 000 kappaletta. Rakennuspalikoiden stabiiliudesta johtuen ne saattavat olla tärkeitä proteiinien fysikaalisen mallinnuksen tutkimus- ja vertailukohteina. Käytännön kannalta työn lupaavin tulos oli se, että rakennuspalikoita löytyi eri vasta-aineiden rakennetiedostoista. Ehkäpä juuri vasta-aineita voitaisiin suunnitella työssä esitetyillä menetelmillä.
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(Helsingin yliopistoUniversity of HelsinkiHelsingfors universitet, 2002)
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(2015)Tutkielmassa tarkastellaan röntgenemissioon perustuvan PIXE-menetelmän soveltuvuutta arkeologisten näytteiden tutkimukseen ja alkuaineanalyysin toteuttamiseen. Esimerkkitutkimuksena esitellään otteita nuorakeraamiselta ajalta peräisin olevien keramiikkanäytteiden analysoinnista. Keramiikan lisäksi tutkielma esittelee monipuolisesti erilaisia arkeologian tutkimuskohteita sekä kyseisten kohteiden tekniikalle asettamia haasteita ja vaatimuksia. Arkeologisen tutkimuksen piiriin kuuluvat muun muassa erilaiset keramiikka- ja metalliesineet, kuten myös maalaukset, pergamentit ja vanhat postimerkit. Erilaisten kohteiden tutkimukseen on olemassa erilaisia PIXE-sovelluksia, kuten fokusoidut ionisuihkut sekä ulkoinen hiukkassuihku, jotka mahdollistavat jopa hyvin hauraiden ja kooltaan vaihtelevien näytteiden tutkimuksen. Kyseisten sovellusten lisäksi tutkielmassa esitellään lyhyesti muita tekniikoita, joiden käyttö on mahdollista joko PIXE-menetelmän rinnalla tai itsenäisesti vastaavanlaisissa mittauksissa. Erilaisia absorbaattoreita käyttämällä voidaan säädellä tutkimustulosten tarkkuutta ja luotettavuutta PIXE-mittausten yhteydessä. Kokeellisen tutkimuksen osalta tutkielmassa keskitytään erityisesti absorbaattorin valintaan sekä näytteen varauskertymän merkitykseen mittaustulosten kannalta. Myös spektrin analysointia ja piikkien tunnistusta tarkastellaan analysointiin soveltuvian ohjelmiston, AXIL:n avulla.
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(2016)Quantum Neural Networks (QNN) were used to predict both future steering wheel signals and upcoming lane departures for N=34 drivers undergoing 37 h of sleep deprivation. The drivers drove in a moving-base truck simulator for 55 min once every third hour, resulting in 31 200 km of highway driving, out of which 8 432 km were on straights. Predicting the steering wheel signal one time step ahead, 0.1 s, was achieved with a 15-40-20-1 time-delayed feed-forward QNN with a root-mean-square error of RMSEtot = 0.007 a.u. corresponding to a 0.4 % relative error. The best prediction of the number of lane departures during the subsequent 10 s was achieved using the maximum peak-to-peak amplitude of the steering wheel signal from the previous ten 1 s segments as inputs to a 10-15-5-1 time-delayed feed-forward QNN. A correct prediction was achieved in 55 % of cases and the overall sensitivity and specificity were 31 % and 80 %, respectively.
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(Helsingin yliopistoHelsingfors universitetUniversity of Helsinki, 2007)ALICE (A Large Ion Collider Experiment) is an experiment at CERN (European Organization for Nuclear Research), where a heavy-ion detector is dedicated to exploit the unique physics potential of nucleus-nucleus interactions at LHC (Large Hadron Collider) energies. In a part of that project, 716 so-called type V4 modules were assembles in Detector Laboratory of Helsinki Institute of Physics during the years 2004 - 2006. Altogether over a million detector strips has made this project the most massive particle detector project in the science history of Finland. One ALICE SSD module consists of a double-sided silicon sensor, two hybrids containing 12 HAL25 front end readout chips and some passive components, such has resistors and capacitors. The components are connected together by TAB (Tape Automated Bonding) microcables. The components of the modules were tested in every assembly phase with comparable electrical tests to ensure the reliable functioning of the detectors and to plot the possible problems. The components were accepted or rejected by the limits confirmed by ALICE collaboration. This study is concentrating on the test results of framed chips, hybrids and modules. The total yield of the framed chips is 90.8%, hybrids 96.1% and modules 86.2%. The individual test results have been investigated in the light of the known error sources that appeared during the project. After solving the problems appearing during the learning-curve of the project, the material problems, such as defected chip cables and sensors, seemed to induce the most of the assembly rejections. The problems were typically seen in tests as too many individual channel failures. Instead, the bonding failures rarely caused the rejections of any component. One sensor type among three different sensor manufacturers has proven to have lower quality than the others. The sensors of this manufacturer are very noisy and their depletion voltage are usually outside of the specification given to the manufacturers. Reaching 95% assembling yield during the module production demonstrates that the assembly process has been highly successful.
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(2018)The human brain is divided into left and right hemisphere, and there are functional differences between the hemispheres. A hemispheric difference is called the lateralization of the brain function, and the degree of lateralization is described by the laterality index. The most investigated domain of the lateralized brain functions is language, which is a left hemisphere dominant function in the majority of the population. Functional magnetic resonance imaging provides a noninvasive method for studying the brain functions indirectly through the bloodoxygenation-level-dependent effect. The language-related functional magnetic resonance imaging can be used in the localization of the Broca’s speech area and determination of the dominant hemisphere in epileptic patients. The purpose of this thesis is to assess a method for calculating the laterality index from functional magnetic resonance imaging data. The data is acquired during three language task paradigms with five subjects and analyzed statistically. The methods used for the laterality index calculations are reviewed, and a new calculation method is presented. Result tables of laterality indices and hemispheric dominances per used regions of interest are generated. The presented laterality index calculation method successfully determined the speech laterality of three subjects out of five as a left hemispheric dominance. The language laterality of two subjects was not successful due to corrupted functional data and contradicted results between different paradigms. The major source of error is the subject’s head motion during the functional imaging. Together with the information about the head motion’s extent, the generated table could provide relevant extra information to epileptic patients’ functional magnetic resonance imaging data and could serve for clinical purposes in the future.
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(2017)Interfaces of solid and liquid helium exhibit many physical phenomena. At very low temperatures the solid-liquid interface becomes mobile enough to allow a periodic melting-freezing wave to pro-pagate along the surface. These crystallization waves were experimentally confirmed in ^4He decades ago, but in ^3He they are only observable at extremely low temperatures (well below 0.5 mK). This presents a difficult technical challenge to create a measurement scheme with very low dissipation. We have developed a method to use a quartz tuning fork to probe oscillating helium surfaces. These mechanical oscillators are highly sensitive to interactions with the surrounding medium, which makes them extremely accurate sensors of many material properties. By tracking the fork's resonant frequency with two lock-in amplifiers, we have been able to attain a frequency resolution below 1 mHz. The shift in resonant frequency can then be used to calculate the corresponding change in surface level, if the interaction between the fork and the helium surface is understood. One of the main goals of this thesis was to create interaction models that could provide quantitative estimates for the calculations. Experimental results suggest that the liquid-vapour surface forms a column of superfluid that is suspended from the tip of the fork. Due to the extreme wetting properties of superfluids, the fork is also coated with a thin (∼ 300 Å) layer of helium. The added mass from this layer depends on the fork-surface distance. Oscillations of the surface level thus cause periodic change in the effective mass of the fork, which in turn modulates the resonant frequency. For the solid-liquid interface the interaction is based on the inviscid flow of superfluid around the moving fork. The added hydrodynamic mass increases when the fork oscillates closer to the solid surface. Crystallization waves below the fork will thus change the fork's resonant frequency. We were able to excite gravity-capillary and crystallization waves in ^4He with a bifilarly wound capacitor. Using the quartz tuning fork detection scheme we measured the spectrum of both types of waves at 10 mK. According to the interaction models developed in this thesis, the surface level resolution of this method was ∼ 10 μm for the gravity-capillary waves and ∼ 1 nm for the crystallization waves. Thanks to the low dissipation (∼ 20 pW) of the measurement scheme, our method is directly applicable in future ^3He experiments.
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(2016)Ilmakehätutkimuksessa ilmanpaineliitäntäinen lentoaikamassaspektrometri nitraattivaraimella (NO3-CI-APiToF) on osoittautunut hyväksi instrumentiksi ilmakehän hivenkaasujen mittauksessa. Alustavat kokeet ovat osoittaneet sen soveltuvan myös räjähdysaineiden mittaamiseen vastaavina hivenpitoisuuksina. Tämän työn tavoite on osoittaa menetelmän käyttökelpoisuus realistisissa olosuhteissa eri räjähdysaineille. Lisäksi vertailtiin kolmea erilaista varauslaitekonfiguraatiota: ilmakehätutkimuksessa käytettyä sekä kahta erilaista yksinkertaistettua mallia. Lähestymistapa oli käytännönläheinen: eri räjähdysaineille määritettiin havaintorajat taustallisessa ja aikarajoitetussa mittauksessa. Havaintorajalla tarkoitetaan pienintä todellista pitoisuutta, mikä voidaan erottaa 95% varmuudella taustamittauksesta yhdellä 12 sekunnin mittauksella. Tutkitut räjähdysaineet 1,3,5-trinitroperhydro-1,3,5-triatsiini (RDX), pentaerytritolitetranitraatti (PETN), trinitrotolueeni (TNT), triasetonitriperoksidi (TATP) ja heksametyleenitriperoksididiamiini (HMTD) ovat kaikki voimakkaita yksikomponenttiräjähdysaineita, jotka edustavat erilaisia kemiallisia rakennetyyppejä. Näytekaasu tuotettiin kiinteästä räjähdysainepinnasta olettamalla kaasun saavuttavan tasapainohöyrynpaineen generaattorin matkalla. Aineet applikoitiin liuoksina teräksisen (RDX, PETN, TNT) tai polyeteenisen (TATP, HMTD) tukilangan päälle. Osa näytteistä ostettiin (PETN, TNT) ja osa syntetisoitiin (RDX, TATP, HMTD). Havaintorajat aineille olivat: RDX 80 ppq, PETN 98 ppq, TNT 84 ppt ja TATP 1,5 ppm. HMTD ei muodostanut havaittavia nitraattiaddukteja. Eri varauslaitteilla ei ollut merkittäviä eroja. Koska havaintorajan määritelmässä on jo otettu huomioon mittauksen satunnaisluonne, näille arvoille ei enää määritetty virherajoja. Tällainen virheraja olisi ns. ‘virheen virhe’. Kaikki räjähdysaineet HMTD:tä lukuun ottamatta pystyttiin havaitsemaan murto-osassa niiden normaalista höyrynpaineesta huoneenlämmössä.
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(2016)Printing drug laden polymer layers is one way to fabricate personalized drug delivery systems. To assure dosage and drug release profiles it is crucial to characterize topography of polymer layers and layer adhesion in multilayer structures. We use our custom build scanning white light interferometer (SWLI) to non-destructively characterize layer thickness, surface roughness and layer adhesion of multilayered drug delivery system. For this work we characterized four drug delivery systems with our SWLI. One of these drug delivery system was characterized inside of microfluidic channel during water discharge. We demonstrated our capability to non-destructively characterize layer thickness of multilayered samples, characterize polymer interface topology with high resolution and distinct between adhesion and delamination on polymer/polymer and polymer/glass interfaces. We also showed our capability to characterize these features in microfluidic channels. We thus demonstrated the possibility to use our device in quality control of tailored drug delivery systems e.g. printed drugs.
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